At 2:21 p.m. Tuesday someone using the Twitter account @Carl_C_Icahn — presumably the corporate raider/hedge fund manager himself — issued the first of a pair of tweets:

That was followed four minutes later by this:

Apple’s (AAPL) shares, which had been trading at $475.77, did what stocks do when Icahn buys them. They went vertical, gaining nearly $9 in less than 3 minutes. By 3:35 p.m. they had touched $494.66.

For those keeping track, that’s a gain in market value of $17 billion in just over an hour.

In a statement to Fortune, an Apple spokesman confirmed that Icahn had been in touch.

“We appreciate the interest and investment of all our shareholders. Tim had a very positive conversation with Mr. Icahn today.”

How many shares Icahn purchased, and what he plans to do with them — besides watch their price rise just because he tweeted about them — remains for now a mystery.

Apple closed at $489.57, their highest price since Jan. 23, having gained $22.21 (4.75%) for the day.